Channel 30 commenced operations on June 8, 1969 as the first UHF television station in the St. Louis market. Though its construction permit was awarded in 1966 by the FCC to a group of local investors under the banner Greater Saint Louis Television Corporation,[1] the station was signed-on under the ownership of Evans Broadcasting, a New York City-based company which acquired the permit in 1968.[2] Initially KDNL-TV ran a format of business news, religious shows, rejected network programs from NBC affiliate KSD-TV (channel 5, now KSDK) and then-ABC outlet KTVI (channel 2), and classic movies. By 1976, the station's schedule became more of the then-standard for independent stations of the era, including cartoons, sitcoms, and movies in primetime and late nights. Also in 1976, KDNL began televising St. Louis Blues hockey games, which ran on the station for five seasons.

In 1977, the business news programming was gradually eliminated and made way for the addition of a few more second-hand classic sitcoms. The Japanese English dubbed shows were phased out as well. The station finally adhered to a more conventional independent format, but its viewership was far behind that of established independent KPLR-TV (channel 11), as KDNL's big disadvantage that at the time was it was the only UHF station in St. Louis.

In March 1981 Evans Broadcasting agreed to sell the station to Atlanta-based Cox Enterprises.[3][4] On June 1, 1982, not long after Cox took control of the station, subscription television service Preview began running on KDNL-TV during the nighttime hours, leaving KPLR-TV as the only full-time independent station in the St. Louis market. Preview was dropped nine months later, and the station resumed running the usual primetime fare of movies and classic sitcoms until 1 or 2 a.m. Channel 30 regained the broadcast rights to the Blues in 1983 for an additional three seasons. In 1984, cartoons were added to the lineup and the station cut back on religious shows. Also under Cox ownership, the station won bids to acquire stronger off-network sitcoms.

On October 9, 1986, KDNL-TV (along with then-sister stations in the San Francisco Bay Area and Detroit) joined the Fox Broadcasting Company as a charter affiliate,[5] eventually branding as Fox 30 by the early 1990s. The station was still programmed essentially as an independent as Fox would not air a full week's worth of programming until 1993. Still, during this time, it began edging closer to KPLR-TV in the ratings after having been well behind channel 11 for most of its first two decades on the air. In 1989, Cox sold channel 30 to St. Louis-based River City Broadcasting, a new company formed by two former KPLR-TV employees.[6]

In 1994, New World Communications bought St. Louis' longtime ABC affiliate, KTVI, and threeotherstations from Argyle Television. New World had signed an affiliation deal to switch the majority of its stations, including KTVI, to Fox.[7] ABC originally wanted to affiliate with longer-established KPLR. However, that station opted to affiliate with The WB instead. More or less by default, ABC cut a deal to affiliate with KDNL and moved its programming there on August 7, 1995. Soon after joining the network, KDNL began showing UPN programming during the late night hours. Despite its size, the St. Louis market did not have enough commercial stations at the time to support a full-time UPN affiliate. After joining ABC, KDNL began to air more first-run syndicated programs and reduced its reliance on older sitcoms.

In 1996, River City merged with the Sinclair Broadcast Group.[8] KDNL dropped the secondary UPN affiliation in January 1998, leaving the network without an outlet in St. Louis until religious station KNLC (channel 24) joined UPN in May 1999[9] (UPN moved to KPLR a year later; St. Louis did not have a full-time UPN affiliate until East St. Louis-based WRBU (channel 46) joined the network in April 2003).

In November 2004, KDNL preempted ABC's telecast of the film Saving Private Ryan, following the lead of other Sinclair-owned ABC affiliates, over concerns regarding the violent battle scenes and graphic profanity that were left intact as ABC aired the film uncut (this occurred nine months after the Super Bowl XXXVIIIhalftime show controversy).[10] Sinclair refused to allow Charter Communications to carry KDNL's high definition signal until April 19, 2007 (when KDNL-DT began airing on Charter digital channel 780 as part of a three-year national retransmission agreement between Sinclair and Charter),[11] making the station the longest holdout in the area to make its high definition digital feed available on the provider (not counting CBS affiliate KMOV pulling its HD signal from Charter in January 2007).

ABC extended its affiliation agreement with KDNL and Sinclair's other ABC affiliates for five years on September 30, 2014, which will keep KDNL affiliated with the network until at least August 2020; as of 2014 Sinclair is now the largest ABC affiliate group, making it unlikely the station will lose the network in the near future.[12]

On October 1, 2010, KDNL began carrying TheCoolTV on digital subchannel 30.2; it carried the music video network until Sinclair dropped TheCoolTV from 32 of its approximately 70 stations at the time on August 31, 2012.[14] On October 28, 2010, KDNL began to carry The Country Network (now ZUUS Country) through a separate affiliation agreement with Sinclair, until some point in summer 2014, it was carried on digital subchannel 30.3.[15][16] In July 2014, KDNL reactivated 30.2 to carry the classic movie network GetTV. In late December 2014, KDNL reactivated 30.3 to carry the male-oriented network Grit.

KDNL-TV shut down its analog signal, over UHF channel 30, on February 17, 2009, the original date in which full-power television stations in the United States were scheduled to transitioned from analog to digital broadcasts under federal mandate (the official date was pushed back to June 12). The station's digital signal remained on its pre-transition UHF channel 31.[17] Through the use of PSIP, digital television receivers display the station's virtual channel as its former UHF analog channel 30.

KDNL aired hourly news cut-ins during regular programming for most of its first 25 years on the air. Shortly before agreed to affiliate with ABC in 1994, KDNL established a full-scale news department. Initially, KDNL offered a nightly local news program at 9 p.m. that debuted on January 1, 1995. The program's original anchors were Jim Wicks (who came to St. Louis from Winnipeg, Manitoba, Canada) and Leslie Lyles (who had been anchoring in Charleston, South Carolina).

When the station switched to ABC seven months later on August 7, the station expanded its news programming; it added newscasts at 5 p.m. daily and at 6 p.m. weeknights, along with weekday morning cut-ins during Good Morning America; the 9 p.m. newscast was also moved to 10 p.m. At the same time, the station fired Wicks and hired longtime KTVI anchor/reporter Don Marsh to join Leslie Lyles on the weeknight newscasts. Ratings plummeted and did not even approach those of KTVI during its latter tenure as an ABC affiliate. The first Nielsen sweep month in the fall averaged only a 2 rating and 5 share. KDNL's newscasts were never competitive with KMOV, KSDK (both have had at least 20% shares over the years), or even KTVI due to the fact that many of the station's on-air staffers came from out-of-town and were unfamiliar with viewers. In KDNL's defense, the station was unable to hire locally since talent on competing stations had either six month or one year non-compete clauses in their contracts. The early evening newscast on weeknights had its time slot fluctuate between 5 and 6 and was even canceled outright for a time. Turnover in the newsroom was very high and this showed in the ratings.

In the spring of 2001, a transmitter failure left KDNL off-the-air for a number of days (or at least broadcasting at a lower power than it did normally). What little audience its newscasts had ended up switching to other sources and never returned. The station finally shut down its news department altogether on October 12, 2001. For the next nine years, KDNL was one of the very few major network affiliates that did not air any local newscasts, with the only news programming on the station consisting of national news programs from ABC News. Until January 2011, the station had been the largest major network affiliate in terms of market size without any local newscasts (CBSO&OWWJ-TV in Detroit was the largest until May 5, 2009, when it launched a now-canceled weekday morning show that was originally produced in partnership with the Detroit Free Press). Most major network affiliates are contractually obligated to air local news, but KDNL's affiliation agreement does not have such a clause.

KDNL occasionally employs its former news set for commentary on sporting events. It also airs local weather cut-ins on weekday mornings during Good Morning America. These updates were formerly compiled and presented by meteorologist Tony Pagnotti at Sinclair's News Central headquarters in Hunt Valley, Maryland. The forecasts are now compiled and presented from Columbus, Ohio sister operation WSYX/WTTE by those stations' evening meteorologists.

On January 3, 2011, NBC affiliate KSDK began producing weeknight 5 and 10 p.m. newscasts for KDNL through a news share agreement. Both broadcasts aired in high definition from a virtual set at KSDK's Market Street studios in Downtown St. Louis and required the hiring of additional personnel.[19] KDNL general manager Tom Tipton stated that the station did not want to run simulcasted or repurposed newscasts in its efforts to return daily news broadcasts to the station. The KSDK-produced newscasts on KDNL were pre-taped in advance.[20] There was no sports report featured during the program. The news share agreement between the two stations was quite unusual given the rarity of a Big Three network affiliate producing newscasts for another Big Three station. In this case, KDNL and KSDK competed against one another in both timeslots. Although KDNL only aired local news programming on weekdays, the station did air replays of KSDK's entertainment/features program Show Me St. Louis on weekends. The agreement with KSDK was to end on December 31, 2013,[21] however the last newscast produced by KSDK aired on January 31, 2014. On February 3, 2014, the 5 and 10 p.m. newscasts were respectively replaced with Family Feud and Who Wants to Be a Millionaire.

On February 10, the St. Louis Post-Dispatch reported that the station intended to restart an in-house news department, with 5 and 10 p.m. newscasts slated to be anchored by KFTK (97.1 FM) morning host and former KMOV reporter Jamie Allman.[22] On November 24, 2014, KDNL officially announced that it would launch its new news program, The Allman Report, in January 2015. KDNL and Allman described the program as an extension of his radio show, with a conservative, "debate-driven format" that focuses on local headlines and issues. The Allman Report originates from the studios of Pelopidas in Brentwood rather than from KDNL's facilities.[23]